Graphics controllers are used in a wide variety of applications to enhance graphics processing and display capabilities for devices such as laptop computers, desktop computers, portable communication devices and other devices having displays. Some computer units and communication devices allow connection to multiple display devices. For example, a graphics controller may provide display data to a cathode ray tube (CRT) monitor, a liquid crystal display (LCD) monitor, or other types of monitors. The differing refresh rates and resolutions of the differing multiple display devices must be accounted for by the graphics controller to suitably display image data simultaneously on multiple display units.
Monitor detection standards are typically classified into three types: DDC2B, DDC1, and others. Typically upon initialization, a graphics controller chip or other controller communicates in a standard serial monitor detection communication protocol such as I2C (DDC1, and DDC2B protocols), or in a non-DDC protocol (such as may be used by Apple Computer® Company based monitors) to facilitate monitor detection. For example, with Inter-IC Control (I2C) monitor detection protocol developed by Philips Semiconductor in about 1995, the graphics controller chip (serving as a master controller) initiates commands or requests to a CRT (which serves as a slave device) to detect the type of monitor. The CRT responds indicating resolution information and other information necessary for the graphics controller chip to suitably generate display data for the display device. One mechanism for monitor detection includes the use of a register based monitor detection interface to be used to facilitate this communication. Data registers are used to facilitate serial to parallel conversion to or from the graphics controller with the display device. A direction register controls the direction of input/output ports on the graphics controller to suitably communicate to allow the graphics controller to detect the type of display device being connected with the graphics controller. The registers and control are typically located on the graphics chip and dedicated to the monitor detection function.
Systems are known that have a graphics controller chip that provides data to multiple differing display devices. Generally, a two-line (two pin) connection is made between the multiple display devices and the graphics controller chip. One line is used for serial data and the other line is used for a serial clock signal. Also, when attempting to display information from a single data source over multiple displays, ratiometric expansion must typically be used to interpolate, stretch or scale the image on a screen having a larger resolution.
Many graphics controller chips have been sold that were originally designed for digital display outputs without a companion chip such as a chip serving as a ratiometric expander that may be needed for expanding data to accommodate display on different resolution displays. With the desire for companion chips, it is desirable to have control over such as chip without requiring additional pins while maintaining the original monitor detection capability.
Consequently, a need exists for a device and method to facilitate serial communication between a display data source and a plurality of display devices where differing protocols may be used for the different types of display units. It would be desirable if such a device could be connected to existing graphics controller chips to facilitate monitor detection with a plurality of different types of display devices and to allow use of existing monitor detection pins in a multipurpose fashion to control a companion circuit (or chip) and to support a plurality of different types of display devices in addition to multi-pin monitor detection. In addition, it would be desirable if such a device minimized interface complexity to facilitate a smaller circuit size to reduce cost and improve reliability.